Off-peak water heating system



Dec. 16, 1941. c. M. OSTERHEL D OFF-PEAK WATER HEATING SYSTEM 2 Sheets-Sheet 1 Filed May 20, 1940 INVENTOR CLARkMOSTER/fl BY ATTORNEY Patented Dec. 16, 1941 OFF-PEAK WATER HEATING SYSTEM Clark M. Osterheld, Stoughton, Wis., assignor to McGraw Electric Company, Elgin, 11]., a corporation of Delaware Application May 20, 1940, Serial No. 336,086

Claims.

My invention relates to fluid heating systems and more particularly to off-peak water heating systems.

An object of my invention is to provide a relatively simple and efllcient off-peak Water heating system adapted particularly to domestic water heaters.

Another object of my invention is to provide relatively simple and inexpensive means for delaying the energization of the heater of a water tank for a predetermined fixed length of time after the start of the oii-peak period in case part of the water in the tank is hot.

Another object of my invention is to provide a water heating system that will effect heating of the water in the tank during the off-peak period only and at substantially the mid-portion of said period.

Still another object of my invention is to provide an off-peak water heating system that will start heating of the water either at the beginning of the off-peak period or after a certain fixed time delay depending on the amount of hot water remaining in the tank at the beginning of the oil-peak period and that will stop heating of the water by thermostatic means before the end of the off-peak period.

Other objects of my invention will either be apparent from a description of several forms of systems embodying my invention or will be pointed out in the course'of the description of these-systems and particularly pointed out in the appended claims.

In the drawings,

Figure 1 is a horizontal sectional view through a domestic hot water tank to which my system I has been applied, taken on the line l-l of Fig. 2,

Fig. 2 is a view in vertical section through a domestic hot water tank, the system embodying my invention being shown schematically therewith,

Fig. 3 is a modified system also embodying my invention,

Fig. 4 is a still further modification of a system embodying my invention,

Fig. 5 is a diagrammatic representation of the ordinary current load on a central station during on-peak and during oiT-peak hours,

Fig. 6 is a front view of a timer dial which is driven by a synchronous electric motor, and,

when the entire load on the central station is a minimum. Under these conditions of low load on its circuits the central station can aflford to sell current at much lower rates than those prevailing during the so-called on-peak period of the day.

Referring now to Figs. 1 and 2 of the drawings, I have illustrated a domestic hot water tank 2| which is usually of circular shape and of much greater vertical axial length than. its diameter. A tank of this kind may be provided with a cold water inlet pipe 23 and a hot water outlet pipe 25 and while I have shown these as extending axially or longitudinally of the tank, I do not desire to be limited thereto since other details as to the cold water inlet and valves, etc. may be provided, all in a manner now well known in the art. I have found it desirable to provide means -whereby the inflowing cold water entering through the pipe 23 will have its force reduced as by a baflle 21, shown in Fig. 2 of the drawings, so as to preventmixture of the cold water entering at the bottom of the tank, with the hot water still remaining in the upper part of the tank. I

I may provide an outside thin sheet metal caseing 29 around the tank 2| and fill the space therebetween with any suitable or desired kind of heat insulating material 3|, now well known in the art. I may provide a plurality of supports 33 on which the tank and its casing may be mounted and the lower end of the tank may be spaced from the lower wall of the casing by 'a plurality of heat insulating blocks 35, all in a manner well known in the art.

I prefer to provide an electric heater 3! which may be of any suitable or desired kind but preferably is of the kind disclosed and claimed in my copending application Serial No. 284,881 filed July 17, 1939. An electric heating element of this kind is'removably positioned within a tunnel member 39, all as set forth in my above mentioned copending application.

Referring now to Fig. 2 of the drawings, I have there illustrated a timing means which, for

if so desired on-the part of the central station to whose circuits the system embodying my invention may be connected. The motor 63 may drive the disc M as through a worm 49 or in any other way, it being understood that the disc 51! is rotated through one full revolutionin twenty-four hours, or once each day.

The disc at is mounted on a shaft 5! which has mounted at its other end a second disc 53 which disc has different radial dimensions overits periphery. Thus the portion 55 has a relatively large radius and its peripheral length is such that it covers substantially one-third of the total periphery or in other words, its peripheral extent is equal to substantially that of theofi-peak period, for purposes of illustration this being assumed to be an eight-hour period, A second portion 5'! of relatively smaller outer radius, has a peripheral extent equal to substantially four hours, a third portion 59 is of still shorter radius and has a peripheral extent of two hours, and a fourth portion 6| has the-same outer radius as portion 511 and is of ten hours in peripheral extent. I .wish to point out here that my invention is not to be considered as being limited to the'use of a separate disc, as it is obvious that the timer dial 68 may have a periphery of differmeans has been shown for'adjusting the position of the disc 53 relatively to the disc 4!, I desire it to be understood that the mounting of disc 53 on shaft 5| is suchasto permit .of doing so, so

that the service man of the central station can so mount the disc 53 on shaft 5! as to have portions thereof alined to agree with the off-peak time period considered proper by said central station. I desire also to point out that the pe-- ripheral extents of several cam surfaces 55, 51, 59 and. 6! may be varied in accordance with the Coil 89 is provided with the usual armature core adapted to energize and cause movement of a contact arm 93 which cooperates with a fixed contact 95 to control the circuit of the electric heatert'l. It will be noted that contact arm 93 engages fixed contact 95 when coil 89 is deenergized.

Contact arm 93 is connected through a. conductor 9? with contact arm 55. Contact member 95 is connected through a conductor 99 with .the movable contact arm 98E of a thermostatically controlled main switch including in addition to the biased resilient contact arm mi a exit outside radii as above described for disc 53.

contact arm 55 normally out of engagement with each other, which latter is adapted to be operatively engaged .by the peripheral surface of disc 53, the portion 55 thereof causing it to be moved, against its normal bias, into contacting engagement with contact arm 55 to thereby close said switch and to prepare the heater circuit so that it may be closed for energization of the heater by other means now to be described.

A thermostatically controlled switch designated generally by the numeral 61 comprises a tube 55 which is closed at its inner end and which has its outer and connected with the tank extending therethrough through a suitable openin provision being made to make the connection rounds the tube 69 the contact arms 13 and 15 will be caused to engage each other and close a circuit now to be described.

substantially fixed contact arm I03. A tubular metal member 085 similar to tubular member 55 extends through the wall of tank 2! to whichit is secured in a leak-proof manner and houses an expansion rod it? which is adapted to engage and move contact arm it! in such manner that arms mi and i133 engageleach other when the water surrounding tube 955 is cold. It may here be pointed out that I prefer to locate the thermostatically controlled switch comprising contacts HM and W3, as well as the thermal actuating means therefor, in the lowermost part of the tank so that they will respond to the temperature of the water in the lowermost part of the tank and cause opening of the circuit through the electric heater 8? when substantially all of thewater in the tank 2!! has been heated to a predetermined temperature. While I have shown the tube 69 as located substantially in the -mid-portion of the vertical dimension or length of the tank 26,1 do not desire to be limited thereto since I may mount it higherup in the tank than shown in Fig. 2 of the drawings or farther down in the tank than as shown in Fig. 2

' of the drawings, all as may be found desirable or gaged from each other and when hot water sur- A substantially fixed "rigid contact arm 11 00- I operates with a resilient contact arm l9. which isv normally biased into engagement with contact arm TI but has its position controlled relatively called for according to the particular problem of the central station desiring to use my. invention as regards their already connected load or as regards the off-peak heating system which they may desire to use.

Contact am I03 is'connected to one terminal of heater 3'! while'the other terminal of heater 3? is connected through a-conductor I08 to lead thereto by a lug 8| secured to the outer endof 'arm 79 by the cam surfaces of rotating disc 53 revolution in twenty-four hours. 'While no The position of disc 53 as shown, in the drawings is that occupied by it at the beginning of the offpeak period, which, for purposes of illustration,

has been assumed to. have a duration of eight hours and to begin say at 10 p. m. and to extend therefore to 6 a. m. the next morning. It will be noted that the engagement of contact arm 55 with the leading end of portion 55 of disc 53 has closed the switch comprising arms 53 and 65 it being understood that the disc 53 rotates in a clockwise direction, as shown by the arrow on the disc. The main switch has therefore been closed and has prepared the circuit through the electric heating means 31. If, now, the upper part of the tank is filled with hot water of a temperature to cause closure of the switch comprising contact arms 13 and 15, it will be evident that since contact arms 11 and 19 are also in engagement at this time, that coil 89 is traversed by a current, the circuit therethrough being substantially as follows: lead 45, contact arms 63 and 55, conductor 85, contact arms TI and 19, conductor 83, contact arms 15 and 13, conductor 81, coil 89 and conductor 9| to supply circuit 41. This will energize the coil and cause it to move contact arm 93 upwardly to substantially the position in Fig. 2 of the drawings whereby the main energizing circuit of heater 3! is interrupted by the contact arms 93 and 95. As abovenoted, this is in case the upper part of the tank andpartic'ularly that predetermined part thereof filled with water immersing the tube 89, has a temperature high enough to cause closure of the switch controlled thereby.

Peripheral portion 59 of cam 53 is shown as having a peripheral extent equal to two hours of time and if no water is withdrawn from tank 2| during this two-hour period, the main heater 31 will remain deenergized during this length of time. At twelve oclock a. m. the lug 81 will start to ride on the surface 6| of the disc 53 whereby contact arm 19 is disengaged from contact arm I1 and the energizing circuit through relay 89 is interrupted with the result that the energizing circuit through the heater 3'! which was prepared, as above stated, by closure of the first main switch comprising contact arms 63 and 65, will then be fully closed, the heater energized and heatingof the water in that part of the tank below tube 69 will start.

I wish to here state that while I have shown the peripheral extent of portion 59 as being equal to two hours, I do not desire to be limited thereto and the disc 53 may have the portion 59 of such peripheral extent as to call for a three-hour duration of such maintenance of the energizing circuit through heater 3! in open condition, if so desired.

I wish to further point 'out that the lowermost thermostatically controlled switch is de-' sired to be effective to cause interruption of the energizing circuit through heater 3'! before the end of the eight-hour oflf-peak period when the resilient contact arm would operatively engage portion 51 of disc 53 whereby opening of the switch comprising contact arms 63 and 65 will be eflfected.

Referring now to Fig. 5 of the drawings, I have there shown a load curve I09 with certain assumed current values, the starting time of this curve being five o'clock a.'m. It will be noted that the load value increases to some relatively high value and for illustrating purposes it has been assumed that this maximum load will be reached at substantially seven a. m. and will continue until around eight or nine o'clock at night, when the load value will start to decrease. While I'have illustrated a substantially uniform load curve I am aware that such is not actually the case and that there will be more or less variation from such a uniform load value during the day, this of course, depending upon the particular conditions of demands for current by the loads connected to the circuits.

As noted, a relatively decided drop in load starts at about 10 p. m. and becomes pronounced at say the period from 1 a. m. to 5 a. m. when the load again starts to increase to its maximum at or about 7 a. m. If now we superpose an offpeak water heating load, indicated by the curve II I in broken lines, as extending from 10 p. m. to 6 p. m., the part of curve I09 extending between thehours of 10 p. m. to 6 a. m. will be raised as shown by the broken line H3, so that the lines of the central station will have connected therewith a relatively appreciable load during the usual off-peak period.

Referring once again to the method of operation of the system shown in Fig. 2, it will be noted that if the upper part of the tank, say the upper half of the tank 2|, is filled with hot water, the energization of the heater 3! will be delayed for a predetermined fixed time which may be made two hours, three hours, or some such value, so that the load caused by oil-peak water heating demands will not be added immediately to the relatively high load value existing during the first part of the off-peak time. feature of my invention causes a gradual rise of the hot water heater load on the power lines as indicated by the heater load curve Ill, between the hours of 10 p. m. and 12 a. m., as shown in Fig. 5. If this delay feature were not present, the full water heater load would be superimposed on the power line load .from other demands and would cause an undesirably big peak load on the power line between the hours of 10 p. m. to about 12 a. m. asindicated by the curve H4 in Fig. 5.

I wish to point out also that in case the upper part of the tank 2| is filled with hot water whereby a predetermined fixed time delay of energization of the heater 3'! is efiected, and if during this fixed time a demand for hotwater arises and some hot water is drawn out of the tank so that the tube 69 and the thermal element are subjected to the temperature of relatively cold water, contact arm 13 will be caused to move out of engagement with contact arm 15 whereby the circuit through coil 89 is opened and the coil 89 is deenergized with the result that the second switch comprising contact arm 93 and contact member 95 will be closed and heater 3'! will be energized. It is, of course, obvious that difierent domestic hot water-containing tanks, the heaters of which are connected to the circuits of a central station, may be partly filled with hot water sufiicient to immerse tube 69 therein or they may have only a relatively small quantity of hot water in the upper part of the tank but out of engagement with tubular member 69. It is therefore evident that while some 13 and I5 controlled thereby is subject to the temperature of a predetermined portion of the water in the tank or to the temperature of the water in a predetermined part of the tank and does not in any way respond to the temperature of the water as existing throughout the whole 7 length of the tank nor does it integrate the tem- This delay perature conditions existing in the water over the entire length of the tank.

Referring now to Fig. 3 of the drawings, I have there illustrated a dial 4I driven by a synchronous electric motor 43 through a worm 49, the

dial 4I being mounted on a shaft 5I which carries also a disc II5. This disc has two portions,

.one portion II1 extending over about one-third of the periphery, i. e., its peripheral extent equals eight hours, the outer radius of the second portion II 9 being less than that of portion I I1. Substantially fixed contact arm I2I cooperates with a contact arm I23 the position of which is controlled by the disc II5 which is rotated in a clockwise direction. Contact arm I23 is normallybiased out of engagement with contact arm I2I but has been moved into engagement therewith by reason of operative engagement of arm I23 with the portion II1 of the periphery of disc II5.

Tubular member 69, which is similar to that shown in Fig. 2 of the drawings and which may include a thermally actuable expansion rod 1I,

controls a'resilient contact arm I25 which is adapted to engage with a substantially fixed conend of this conductor being connected with contact arm I23. Contact arm I2I is connected with contact arm I25 by a conductor I31. A contact arm I 39 is electromagnetically controlled by coil 89 and is adapted to be caused to engage a con tact I4I when coil 89 is energized.

Let it beassumed that the upper part, say the upper half of the tank 2|, is filled with hot water so that thermal element 1I will be heated and will have caused contact arm I25 to move out of engagement with contact arm I21 so that the energizing circuit through coil 89, which circuitv extends through contacts I2I and I23, will have been opened so that contact bar I39 will be in the position shown in Fig. 3 of the drawings. It will be noted that in this diagram only one electromagnetically controlled main heater switch is provided and if the upper part and particularly the upper half of the tank is filled with hot water, the energizing circuit through to engage the same when arm I45 operatively engages the portion II1 of disc II5 a certain fixed time after the start of the oiI-peak period.

part of the tank is filled with hot water, the energizing circuit through coil 89 will be closed after a predetermined fixed delay time when contact arm I45 is moved into engagement with contact arm I43 as hereinbefore stated. While I have shown the fixed time of delay of closure of the energizing circuit through heater 31 as being on the order of four hours, I am notlimited thereto since, as shown in Fig. 7 of the drawings, I may mount contact arms I 43 and I45 on a peripherally" adjustable supporting arm I5I so that the operator or service man 'may' easily and quickly adjust the angular position of the two contacts to suitably vary the fixed time of delay, it being understood that the main object of this delay time is to cause the period of energization of heater 31 to fall within the period of off-peak operation when the normally connected load is a minimum which, generally speaking, will be such that the mid-portion of the energization period of the water heater will coincide substantially with the mid-portion of the off-peak period itself.

Referring now to Fig. 4 of the drawings, I have there shown a still further modification of system embodying my invention and those parts which are the same as those shown in Figs. 2 and 3 of the drawings are provided with the same numbers. The shaft 5|, which is driven by a synchronous electric motor 43, has mounted thereon a disc I53 which disc is provided with a portion I55 of larger radius which is relatively short peripherally. Following this portion there is a short peripheral portion I51, of lesser radius, which may be of such extent as to cover about two hours, then a portion I59 of greater. radius, which may be of substantially six hours duration as to time and then a portion IBI which extends I over about sixteen hours total. A relatively fixed contact arm I63 has a spring contact arm I65 cooperating therewith, the latter arm being normally biased out of engagement with arm I63 except when. it is operatively engaged by the portions I and I59 of the disc I53 which is heater 31 is not closed at the time that contact arm 123 is moved into engagement with contact arm I2I at the beginning of the oiT-peak period when disc H5 is in the position shown in Fig. 3 of the drawings.

It is further obvious that if the upper .part, say the upper half of the tank, is filled with cold water, contact arm I 25 will be in engagement with contact arm I 21 and the energizing circuit through relay coil 89 will have been closed at the start of the off-peak period so that contact arm I39 will engage contact I4I to thereby energize heater 31.

I provide also means for causing closing of the energizing circuit through :heater 31. by means of switch arm I39 and contact I, this means including a contact arm I43 and a cooperating contact arm I45 which latter is normally biased out of engagement with arm I43 but is caused caused to turn in a clockwise direction the same as hereinbefore described for the contact actuating discs in the other figures of the drawings.

Supply circuit lead 45 is connected to contact arm Ithrough a conductor I61 and contact arm I63 is connected through a conductor I69 to one terminal of a relay coil "I, the other terminal of which is connected through a conductor I 13 and another conductor I15 with the other supply circuit lead 41. When the disc I53 is in the position shown in Fig. 4 of the drawings,

which positionit is intended to occupy at the beginning of the off-peak period, the energizing circuit through relay coil "I will be closed and a contact arm I11 will be moved upwardly into the position shown in the broken lines where it will-engage a contact member I19 which is connected to conductor I69 through a short conductor I8I.

An auxiliary thermally controlled switch comprising the thermal element II in tube 69 is also provided and controls a spring contact arm 13 forcing it into engagement with contact arm 15 tact arm "II of the thermal circuit controller subjected to the temperature of the water in the lowermost part of the tank, said thermal controller including particularly the expansion bar I01. Contact arm I63 is connected through a conductor I85 with one terminal of heater-31, the other terminal of which is connected through a conductor I81 with conductor I15 and therefore to the other supply circuit lead 41. Contact arm 13 is connected through a conductor I99 with one terminal of a second relay coil I9I, the other terminal of which is connected through a conductor I93 with conductors I13 and I15. Rela-y coil I 9I energizes and controls a pivotally supported latch member I95 which is of substantiallyhook shape and is adapted to cooperate with and hold contact arm I11 in engagement with contact arm I19 when coil ISI is deenergized.

Let it be assumed that the parts of the apparatus shown in Fig. 4 of the drawings are in th positions shown, i. e., contact arms I63 and I65 are in engagement because of the projection I55 operatively engaging arm I65. If the upper part of the tank is filled with hot water, contact arms 13 and I5 will be in engagement with each other and relay coil I9I is energized whereby latch member I95 will be moved to the position shown in broken lines so that when contact arm I11 is energized and caused to move to its upper position, shown in broken lines, and into engagement with contact member I19 because of the energization of relay coil I1I, the-latch member I95 will have been moved out of engaging and holding position relatively to contact arm I 11 so that as soon as projection I55 has been moved out of operative engagement with contact arm I65, the energizing circuit through relay moved upwardly into engagement with contact A member I19 it will remain in such position whereby electric heater 31 will be energized at substantially the beginning of the oflE-peak period.

If, as stated before, the upper part and particularly the upper half of the tank, is filled with hot water, energization of the heater 31 will be delayed /a predetermined fixed time the length of which depends upon the peripheral extent of th portion I51- of disc I53 and when contact arm I is operatively engaged by portion I59 of the disc, contact arm I65 will again be caused to engage contact arm I63 whereby coil III is energized and contact arm I11 is caused to move into and is held in engagement with contact member m for the rest of the ofi-peak period which may. be during six hours thereof. However, th details of heater capacity and of the selected that the energizing circuit through heater 31 will be opened by disengagement of contact arms IIiI and I03 before the end of the off-peak period.

It will be noted that in all of the various forms and modifications which I have illustrated and described, the arrangement is such that the electric heater for the hot water tank is effectively deenergized by thermally controlled means although as has hereinbefore been set forth, the other parts of my system are so constructed and adjusted that the time controlled switching means is not effective to cause final deenergization of the electric heating element since to do so would add an undesirable off-peak load to the circuit in addition to the steadily mounting electric heater of a fluid-containing tank as exemplified by the usual domestic hot water receiving tank, which system is efiective to delay energization of the electric heater for a predetermined fixed time, which fixed time of delay is adjustable, in case a predetermined part of the fluid contents of the tank are at relatively high temperature.

The system embodying my invention causes energization of the electric heater at an adjustablefixed time during'the oil-peak period and the heater is deenergized by a thermostatically controlled switch means, the thermostatic element of which is responsive to the temperature of the water in the lowermost part of the tank.

Certain modifications permit of starting energization of the electric heating element if some of the hot water in the upper part of the tank is withdrawn during the hereinbefore mentioned fixed delay period so that the system embodying my invention is operative in the manner described and to finally cause thermally-eifected deenergization of the electric heater before the end of the off-peak period and, as has already been hereinbeforeset forth, the thermostatic means set forth by me is not subject to what may be called an integration of the temperature of entire contents of the tank but is controlled by the temperature of the water in a predetermined part and preferably in the upper portion of the tank which, as I have found, is that portion containing any hot water which may have been left from the preceeding days use of hot water from the tank.

Various other modifications may be mad in V the details of the system embodying my invention without departing from the spirit and scope thereof and all such further modifications for a fluid-receiving tank having an electric length of time during which it may be energized as well as the adjustment of the lowermost thermostatically controlled switch are all so heater, an electric circuit including switching means for controlling said electric heater, a timing means for preparing said electric circuit so that the electric heater may be energized during fixed len th of time, andmeans controlled by said timing means for causing energization of said heater at the end of said fixed length of time.

2. In an ofi'-peak water heating system adapted -for use with a water tank having an electric heater, an electric circuit for said heater including switching means for controlling said electric heater, a timing means for preparing said circuit so that the electric heater may be energized dur-' ing a preselected period of day only and means including a thermostat responsive to the temperature of the water in the upper half of the tank efiective to delay energization of said heater a predetermined fixed length of time after the timing means has prepared said electric circuit when the temperature of the water in the upper half of the tank is above a predetermined value at the time of said preparation of the circuit and remains above said value during said fixed length of time and effective during said fixed length of time to cause energization of said electric heater on reduction of the temperature of the water in the upper half of the tank below said predeter mined value.

3. In an off-peak waterheating system'for a water-containing tank having an electric heater, a first and a second switch connected in series I circuit with each other for controlling said electric heater, clock driven means. for causing closure of said first switch during an off-peak period of predetermined duration and means controlled by the temperature of the water in the upper half of the tank for delaying closure of the second switch for a predetermined fixed length of time after closure of said first switch when the temperature of the waterin the upper half of the tank is above a predetermined value at the time of closure of said first switch and remains above said value during said fixed length of time.

4. In an ofi-peak water heating system adapted for use with a water tank having an electric heater, an electric circuit for said heater including switching means for controlling said electric heater, a timing means for preparing said circuit so that the electric heater may be energized during a preselected period of day only and means 5. In an ofi-peak fluid heating system adapted fora fluid-receiving tank having an electric heater, an electric circuit including switching means for controlling said electric heater, a timing means for preparing said electric circuit so that the electric heater may be energized during a preselected period of day only and thermostatic means responsive to the temperature of the fluid" and when the temperature of the fiuid in the upper part of the tank remains at or above said predetermined value during said, time of delay, and clock-controlled means for causing energization of said electric heater at the end of said fixed length of delay time.

6. In an off-peak water heatingsystem fora water containing tank having an electric heater, afirst and a second switch connected in series circuit with each other for controlling said electric heater, clock-driven means for causing closure of said first switchat the start of and during an off-peak period of predetermined duration and means including a thermostat subject to the temperature of the water in the upper half of the said first switch'and for causing closure of said second switch during said fixed length 01' delay time when the temperature of a predetermined including a thermostat responsive to the temperature of the water in the upper half of the tank and effective to delay energization of said heater a predetermined fixed length of time after the timing means has prepared said electric circuit,

many-controlled switch responsive to. the temperature of the water in the lowermost part of thetank for causing deenergization of said heater when the temperature of substantially all of the water in the lowermost part of the tank has been raised to above said predetermined value.

portion of the water in the upper. half of the tank drops below said predetermined value.

7. In an off-peak water heating system adapted" and a timing means indicating the time of clay, the improvement comprising means driven synchronously with and by said timing means and thermally actuable means responsive to. the temperature of the water in the upper portion of the tank to cause closing of said switching means at a preset time of day when the tank contains less than a predetermined quantity of hot water in the upper portion thereof and to delay closing of said switching means for a fixed length of time when the tank contains more than a predeter-' mined quantity of hot water in the upper portion thereof.

8. In an off-peak water heating system adapted for a water containing tank having an electric heater, an electric circuit including said heater and switching means for controlling said heater and a timing means indicating the time of day, the improvement comprising means driven synchronously with and-by said timing means and thermally-actuable means responsive to the temperature of the water in the upper portion of the tank to cause closing of said switching means at a preset time of day when the tank contains less than a predetermined quantity of hot water in the upper portion thereof and to delay closing of said switching means for a fixed length of time when the tank contains 'more than a predetermined quantity-of hot water in the upper portion thereof and a thermally controlled switching means responsive to the temperature of the water a,2ee,242

in the lower portion of the tank for efiecting deenergization of said electric heater when the lower portion of the tank contains hot water.

9. In an ofi-peak water heating system adapted for a water containing tank having an electric heater, an electric circuit includingsaid heater, a first and a secondswitch in said electric circuit and connected in series circuit with each other for controlling the energization of said electric heater and a continuously operative timing means indicating the time of day, the improvement comprising means driven synchronously with and by said timing means for efiecting closing of said first switch at the beginning of a preset ofi-peak period, and for holding it closed during said period, electromagnetic means for actuating said second switch and means including a thermostat subject to the temperature of the water in the upper portion of the tank for causing said electromagnetic means to close said second switch at the same time that the first switch is closed when the upper portion of the tank contains cold water and to prevent closing of said second switch when the upper portion of the tank contains hot water and means actuated by the means effecting closing of said first switch for causing closing of said second switch by said electromagnetic means a predetermined length of time after closure of said first switch.

10. In an ofi-peak fluid heating system adapted for a fluid-receiving tank having an electric heater, an electric circuit including switching means for controlling aid electric heater, a timing means for preparing said electric circuit so that the electric heater may be energized during a preselected period of day only and means including a thermostat responsive to the temperature of the fluid in a predetermined part of the tank for causing energization of the electric heater to be delayed a fixed length of time after the start of said preselected period of day when the temperature of the fluid in said predetermined part' of the tank is above a predetermined value at the beginning of said preselected period of day and remains above said value during said delay time.

11. In an off-peak fluid heating system adapted for a fluid-receiving tank having an electric heater, an electric circuit including switching means for controlling said electric heater, 9. timing means for preparing said electric circuit so that the electric heater may be energized during a preselected period of day only and means including a thermostat responsive to the temperature of the fluid in a predetermined part of the.

4 tank for causing energization of the electric heater to be delayed a fixed length of time after the start of said preselected period of day when the temperature of the fluid in said predetermined part of the tank is above a predetermined value at; the beginning of said preselected period of day and remains above said value during said delay 1 a first and a second switch connected in series.

circuit with each other for controlling said electric heater, clock driven means for causing closure of said first switch during an off-peak period of predetermined duration and means controlled by the temperature of the water in the upper half 75 for a of the tank for delaying closure of the second switch for a predetermined fixed length of time after closure of said first switch when the temperature of the water in the upper half of the tank is above a predetermined value at the time of closure of said first switch and remains above said value during said fixed length of time and a thermally-controlled switch means responsive to the temperature of the fluid in the lowermost part of the tank for causing deenergization of said electric heater when the temperature of the fluid in the lowermost part of the tank has been raised to a predetermined value.

13. In an oil-peak water heating system for a water containing tank having an electric heater, a first and a second switch connected in series circuit with each other for controlling said electric heater, clock driven means for causing closure of said first switch duringan off-peak period of predetermined duration and means including a thermostat controlled by the temperature of the water in a predetermined part of the tank for delaying closure of the second switch for a predetermined fixed length of time after closure of said first switch when the temperature of the water in thepredetermined part of the tank is above a predetermined value at the time of closure of said first switch and remains above said value during said fixed length of time and for causing closure of said second switch at the yen of said delay time.

14. In an off-peak fluid heating system adapted for a fluid-containing tank having an electric heater, means including an electromagnetic switch controlling the energization of the heater and two switches connected in series electric circuit with each other and controlled respectively in accordance with time and with the temperature of the fluid in the upper part of the tank and jointly'controlling the energization of said electromagnetic switch to delay energization of the heater for an adjustably preset fixed time after the start of an ofi-peak period in case the fluid in the upper part of the tank is hot at the start of an off-peak period and remains hot during said switch controlling the energization of the heater and two switches connected in series electric circuit with each other and controlled respectively in accordance with time and with the temperature of the fluid in the upper part of the tank and jointly controlling the energization of said electromagnetic switch to delay energization of the heater for an adjustably preset fixed time after the start or an oil-peak period in case the fluid in the upper part of the tank is hot at the start of an off-peak period-and remains hot during said preset fixed time of delay, and to cause energization of said heater at the end of said fixed delay time irrespective of the temperature condition of the fluid in the upper part of the tank and thermally-actuable heater control switch means responsive to the temperature of the fluid in the lower part of the tank for causing deenergization of the electric heater in case substantially all of the fluid in the tank is hot before the end of an oil-peak period.

16. In an oil-peak fluid heating system adapted fluid-containing tank having an electric fheater, means including an electromagnetic switch controlling the energization of the heater and two switches connected in series electric circuit with each other and controlled respectively in accordance with time and with the temperature of the fluid in the upper part of the tank and jointly controlling the energization of said electromagnetic switch to delay energization of the heater for an adjustably preset fixed time after the start of an oiI-peak period in case the fluid in the upper part of the tank is hot at the start of an off-peak period and to cause energization of. said electric heater during said delay time in case withdrawal of hot fluid from the tank during said delay time subjects the switch con trolled by the temperature of the fluid in the upper part of the tank to cold fluid.

17. In an oil-peak fluid heating system adapted for a fluid-containing tank having a single electric heater, means including an electromagnetic switch controlling the energization of the heater and two switches connected in series electric circuit with each other and controlled respectively in accordance with time and with the temperature of the fluid in the upper part of the tank and jointly controlling the energization of said electromagnetic switch to delay energization of the heater for an adjustably preset fixed time after the start of an oil-peak period in case the fluid in the upper part ofthe tank is hot at the start electrically connected in shunt to said thermallyactuable switch to cause energization of said electromagnetic switch and energization of said heater at the end of said preset fixed delay time irrespective of the fluid temperature in the upper 10 switch controlling the energization of the heater,

part of the tank. t

19. In an off-peak fluid heating system adapted for a fluid-containing tank having a single electric heater, means including an electromagnetic a continuously operative timing means, a switch controlled by said timing means, a. thermallyactuable switch responsive to the temperature of I the fluid in the upper part of the tank, electric connections between said switch controlled by said timing means, said thermally-actuable switch and said electromagnetic switch to cause said switch controlled by said timing means and said thermally-actuable switch to jointly control the energization of said electromagnetic switch means and electrically connected in shunt to said thermally-actuable switch to cause energization of said electromagn tic switch and energization of said heater at the end of said preset fixed of an off-peak period and remains hot during said preset fixed time of delay, and to cause energization of said heater at the end of said fixed delay time irrespective of the temperature conditionof the,fluid in the upper part of the tank and for causing reenergization of the heater in case of withdrawal of sufiicient hot fluid from the tank during the off-peak period to subject said thermally-actuable heater control switch to cold fluid.

18. In an ofi-peak fluid heating system adapted for a fluid-containing tank having a single eleclay energization of said heater for a preset fixed 55 time after the start of an ofi-p'eak period in case the fluid in the upper part of the tank is hotat the start of an ofi-peak period and remains hot during said preset fixed time of delay and a secdelay time irrespective .of the fluid temperature in the upper part of the tank and thermallyactuable heater control switch means responsive to the temperature of the fluid in the lower part peak periodand for causing reenergization of the heater in case of withdrawal of suflicient hot fluid from the tank during the ofi-peak period to subond switch controlled by said timing means and 6 .ject said thermally-actuable heater control switch to cold fluid.

20. In an ofi-peak water heating system adapted for a water containing tank having an electric heater, an electric circuit including said heater and switching means forcontrolling said heater and a timing means indicating the time of day, the improvement comprising means driven synchronously with and by said timing means and thermally actuable means responsive to the temperature of the water in the upper portion of the tank jointly efiective to cause a preset fixed delay in closing of said switching means after the start of an oiI-peak period in case the tank contains more than a predetermined quantity of hot water in the upper portion thereof and to cause energization of said electric heater as soon as withdrawal of hot water-from the tank during the preset delay period subjects said thermally actuable means to cold water.

CLARK M. OS'I'ERHELD. 

